mcg
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| posted on 7/1/11 at 02:52 PM |
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Air box design input
Hi,
Following a few recent threads on Airboxes, I am going to have a stab at making my own, based on the high cost of purchasing one, and also then I can
make it fit the space I have without having to shred the bonnet. The two things I am trying to achieve are: 1. Best performance, 2. Noise reduction
for track day pruposes.
For the airbox itself I am planning on using large bore tubing and plastic sheet cut and glued.
Could anyone take a look at the pics below and give their thoughts on what is going to be the best solution. The airbox design is pretty much the same
on all options - it is the location of the filter and the pipe sizes that I am not sure on. Option 3 would probably be the easiest to make, but I
wonder if the air flow would be too restricted, and /or the sound deadening would not be sufficient? Any difference having the filter close to the
carbs or closest to the air? The thought on option 4 is to add a 'can' into the line to distort the flow of sound as it moves from the
small space in the pipe to the big space in the 'can', and back to the small space in the pipe.
Any general thoughts or advise would really be appreciated.
[Edited on 7/1/11 by mcg]
[Edited on 7/1/11 by mcg]
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loggyboy
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| posted on 7/1/11 at 03:14 PM |
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Is intake air noise really that much of a contributer to the sound, I would expect the exhaust and engine to be the more likely suspects.
That looks like a ram air design, i seem to recal that doesnt work well with carbs, they dont like being force fed.
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wylliezx9r
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| posted on 7/1/11 at 03:29 PM |
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quote:
Originally posted by loggyboy
Is intake air noise really that much of a contributer to the sound, I would expect the exhaust and engine to be the more likely suspects.
That looks like a ram air design, i seem to recal that doesnt work well with carbs, they dont like being force fed.
Carbs dont like ram air ???? What about on motorbikes, it adds about 10 bhp at high speed ?
I spent a lot of money on booze, birds and fast cars. The rest I just squandered.
George Best
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Bluemoon
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| posted on 7/1/11 at 03:31 PM |
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quote:
Originally posted by loggyboy
Is intake air noise really that much of a contributer to the sound, I would expect the exhaust and engine to be the more likely suspects.
That looks like a ram air design, i seem to recal that doesnt work well with carbs, they dont like being force fed.
Can be, but I think this is from the carb's venturi rather than the filter?
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matt_gsxr
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| posted on 7/1/11 at 03:36 PM |
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Pretty pictures.
I built one a while back (before my recent turbo plans). These are my memories.
You can't have too much airbox volume. Volume slows down the air, which is good as it evens out airflow. I made mine big. The Andy Bates
air-box is big (8litres?), as are the racing airbox upgrades.
I don't think you need to worry about noise coming out of the front of the pipe, it acts as a lowpassfilter which seems to hush things up (so 4
is not necessary).
Put the airfilter where you like, you can blow through them so they normally offer very little resistance.
3inch pipe is big enough to result in no pressure drop on a litre-bike, 2in might be a bit borderline (just do the pressure drop calculations)
I think a big airbox would also help in noise reduction.
Helmholz resonances will get mentioned, but its a bit too tricky to get that working without lots of prototypes and experimentation (I suspect).
So, 1 or 2 but make the airbox bigger would be my suggestion.
Matt
[Edited on 7/1/11 by matt_gsxr]
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loggyboy
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| posted on 7/1/11 at 03:51 PM |
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quote:
Originally posted by wylliezx9r
Carbs dont like ram air ???? What about on motorbikes, it adds about 10 bhp at high speed ?
Bike carbs are designed for it, car carbs arent.
If he is using bike carbs then its not an issue.
[Edited on 7/1/11 by loggyboy]
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MikeCapon
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| posted on 7/1/11 at 04:01 PM |
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Bike carbs or car carbs, it's the same deal. Either will benefit from an increased airbox pressure but ONLY if the airbox is linked to the float
chambers to equalize the pressures. It doesn't take much imagination to work out what happens otherwise...
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smart51
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| posted on 7/1/11 at 04:09 PM |
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Bigger is better and yours looks tiny. Air boxes resonate at a frequency defined by the volume and the shape of the inlet tube. Look up helmholtz
resonators for the simple formula. You can use it for filling in a hole in your torque curve, otherwise set resonance as low as possible. That means
a big box. Big boxes mean less restriction too.
As for noise, I made an induction silencer for mine. It made a big difference. It only makes a difference with the throttle open, but the difference
is obvious. Induction noise is the bark when you put your foot down. If drive by noise is a problem, you need to silence your induction.
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rf900rush
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| posted on 7/1/11 at 04:50 PM |
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Found this LINKY on inlet tuning.
May help.
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RichardK
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| posted on 7/1/11 at 05:10 PM |
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Exactly what I'm making too, I'm doing option 3, just trying to work out how to attach to carbs!
Cheers
Rich
Gallery updated 11/01/2011
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scutter
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| posted on 7/1/11 at 06:11 PM |
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quote:
Originally posted by loggyboy
Is intake air noise really that much of a contributer to the sound, I would expect the exhaust and engine to be the more likely suspects.
My intake noise with a half exposed Pipercross filter is 3Db louder than a 907 exhaust on the zetec. I'll be watching this thread with
interest.
AYB Dan.
The less I worked, the more i liked it.
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mcg
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| posted on 7/1/11 at 06:24 PM |
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Thanks everyone for the inputs. There is only so far that my maths brain can be pushed before it explodes!!!
Interesting point about the volume of the airbox. I was thinking the same, but then saw the pictures of the PX600 Airbox and figured that was quite a
small volume?? Maybe its a larger volume, but as its longer and narrower it disguises its volume!
So what do you think about the PX600 Airbox as a template for a design to copy?
BTW, I'm running a 8v Vauxhall Engine on Fireblade carbs.
Cheers again
Matt
quote:
Originally posted by matt_gsxr
Pretty pictures.
I built one a while back (before my recent turbo plans). These are my memories.
You can't have too much airbox volume. Volume slows down the air, which is good as it evens out airflow. I made mine big. The Andy Bates
air-box is big (8litres?), as are the racing airbox upgrades.
I don't think you need to worry about noise coming out of the front of the pipe, it acts as a lowpassfilter which seems to hush things up (so 4
is not necessary).
Put the airfilter where you like, you can blow through them so they normally offer very little resistance.
3inch pipe is big enough to result in no pressure drop on a litre-bike, 2in might be a bit borderline (just do the pressure drop calculations)
I think a big airbox would also help in noise reduction.
Helmholz resonances will get mentioned, but its a bit too tricky to get that working without lots of prototypes and experimentation (I suspect).
So, 1 or 2 but make the airbox bigger would be my suggestion.
Matt
[Edited on 7/1/11 by matt_gsxr]
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smart51
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| posted on 7/1/11 at 07:30 PM |
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Here are some links to my airbox build: Prototype airbox,
Final Airbox,
Carb Bell Mouths
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matt_gsxr
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| posted on 7/1/11 at 07:38 PM |
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Commercially it makes sense to make an airbox that fits most cars.
I suspect that is why the px600 is quite tight.
If I had a range of 1, then I'd make it small too.
Look at the Reverie site. Mostly bigger
http://www.reverie.ltd.uk/product_list.php?group=A%20AIRB
Matt
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